[Spice_discussion] Long-term accuracy of the IAU_MOON frame

[Ernie Wright]

Thanks John, this is indeed quite helpful.  Uncertainties on the order 
of a kilometer are all but invisible for what I'm doing.  In fact, it 
wouldn't surprise me to discover that I'm abusing SPICE in other ways 
that lead to errors of that order.

Fortunately, I'm not landing a spacecraft.  I just want to be reasonably 
sure that IAU_MOON won't blow up or something.

- Ernie


On 05/10/2015 08:30 AM, John Irwin wrote:
> Ernie,
>
> The following observations may be of help.
>
> Using the ME lunar orientation taken from DE430 (a successor to DE421
> with a longer time span) and comparing it with the IAU_MOON model
> between the years 1550 and 2000, I find there is a general increase
> in the angular difference between these two models the further back
> in time you go. But at most the linear difference is only 299 m on
> the lunar surface (sampling the orientations at 1-day intervals).
>
> Assuming the PA orientation taken from DE431 (a longer version of
> DE430) can be converted to ME using the same offset as DE430, the
> difference in orientation compared to IAU_MOON reaches 630 m going
> back to the year 1000.
>
> Strictly speaking the ME offset for DE431 will not be the same as
> DE430 because of the slightly different modelling of the lunar
> orientation but I cannot see them being vastly different.
> Unfortunately JPL have not determined this offset for DE431.
>
> So I would say the IAU_MOON model performs quite well over several
> hundred years into the past, although it all depends on how far you
> want to go back and whether the above errors are within your
> requirements. If not, perhaps you can get NAIF to create a binary PCK
> from DE430 or DE431 over a longer time span. I think the results
> should be compatible with the DE421 orientation used for LRO data.
>
> John.
>
>
>> Does anybody have a sense of the long-term accuracy of IAU_MOON?
>>
>> - Ernie

-- 
Ernest T. Wright                                ernest.t.wright at nasa.gov
Scientific Visualization Studio                 http://svs.gsfc.nasa.gov
NASA/Goddard Space Flight Center, Code 606.4      voice: +1 301 286-1569
Greenbelt, MD 20771                                 fax: +1 301 286-1634